Carbonization of fibrous rayon



United States Patent Delaware No Drawing. Filed duty 26, 1963, Ser. No. 297,954- 9 Claims. (Cl. 23-2091) This invention relates to the production of carbonized or graphitized fibrous rayon materials having improved properties.

It is well known in the art that rayon fibrous materials, such as rayon filaments or rayon textiles or woven fabrics may be carbonized or graphitized by heating the starting rayon material in an inert atmosphere to suitable temperatures, for example to 800 C. (or to temperatures between about 500 C. and about 1200 C.) to bake or carbonize same, or to 2000-3000 C. to graphitize same.

The prior art also teaches or suggest some different temperature-time conditions or rates in order to carbonize or graphitize rayon. United States Patents 3,011,981 to Soltes and 3,055,775 to Abbott and British Patent 894,458 may be said to be representative of various conditions or rate schedules for carbonizing or graphitizing rayon fibrous materials.

This invention, as previously stated, also relates to the carbonization or graphitization of rayon, but it is most particularly related to a particular step in such processes, which step leads to carbonized or graphitized products of improved quality as compared to the products produced when the step is not carried out, or greatly shortened heating cycles to obtain products of equal or improved quality, or both.

It is a finding of this invention that-if rayon is heated to a temperature within the range of about 325 C. to about 390 C. and more preferably about 340 C. to

or mechanically worked after it has been heated to this temperature and before heating it further-this procedure, viz, interrupting the heating of the rayon at a given point and flexing same, results in end carbonized or graphitized products having properties which are considerably improved over the properties the products have if this step is not carried out, but identical heating procedures and times are otherwise employed; or in greatly decreased heating schedules or processing times to obtain products whose properties are as good as or better than those obtainable only by greatly prolonging the heating cycles. It is important, to achieve these improvements, that the flexing be carried out after the rayon has been heated only to a certain temperature point, not too low nor too high. For example, if the rufiiing is carried out after the rayon has been heated to a temperature of only about 310 C. or lower, the property improvements and processing advantages brought about by rufiling are not realized; nor are they brought about if the rayon has first been heated to too high a temperature, e.g. 410 C. or higher, before it is ruffled or thoroughly flexed. However, the property improvements are generally obtainable in some measure if the step is carried out and the heating interrupted anywhere in the range between about 325 C. and about 390 C. Carrying out of the step after the rayon has been heated to a temperature in the range of about 340 C. to about 360 C. invariably results in some improvement in the properties and these improvements are generally very marked.

The property improvements being referred to as chieveable by the procedures of this invention are improved flexibility and strength of the final carbonized or graphitized products which is not to say that other property improvements are not also obtained by the procedures involved herein. v The following examples set forth in tabular form, further illustrate the invention and contrast it with prior art about 360 C., and 18 then thoroughly flexed or rufl led 40 procedures and results.

TABLE I Properties of Carbonizcd Properties of Graphitized Ex. Starting Material Heating Procedure Flering Step Product (Baked to 800 0.) Product (Graphitized to 1 Viscose rayon Room temp. to 350 C. Flexing carried out after About 0.3 gram/denier About 0.4 gram/denier filaments. 15 minutes, 350 C. to the rayon was heated to tensile strength. Extensile strength. Ex-

800 (LR-10 minutes, 800 350 C. and cooled to cellent flexibility. cellent flexibility. C. to 2,800 C.l0 40 C. minutes. 2 Vis1cose rayon Same as in Example 1 Same as in Example 1 d0 D 3. Saponified acetate do do About 0.4 gram/denier About 0.5 gram/denier rayon filaments. tens le strength. tensile strength.

Excellent flexibility. Excellent flexibility. 4 Saponified acetate do "do do D0.

rayon cloth.

5 Same as in do No intermediate flexing 0.1 Gram/denier tensile 0.1 gram/denier tensile Example 1. step. strength. Flexible. strength. Flexible. 6 Same as in Same as in Example 2. .do do Do.

Example 2. 7 do Room temp. to 310 C.- Flcxing carried out after do Do,

.15 minutes, 310 C. to the rayon was heated to 800 C.-10 minutes, 310 C. and cooled to 800 C. to 2,800" C.10 40 C. minutes. 8 do Room temnto 410 C.-15 Flexing carried out after (lo Do,

minutes, 410 C. to 800 C.- the rayon was heated to 10 minutes, 800 C. to 410 C. and cooled to 2,800 C.10 minutes. 40 C. 9 (lo Room temp. to 350 C.- No intermediate flexing do Do.

minutes, 350 C. to 800 step. C.10 minutes, 800 C. to 2,800 C.-l0 minutes. 10 do Room temp. to 350 C.- do About 0.3 gram/denier About 0.4 grain/denier hours, 350 C. to 400 tensile strength. tensile strength. C.-5 hours, 400 C. to Excellent flexibility. Excellent flexibility. 800 C.-8 hours, 800 C. to 2,800 C.-2 hours.

It will be noted from the foregoing table, particularly Examples 1-4, that carbonized and graphitized products having very good properties are obtainable by the processes of this invention and regardless of whether the starting rayon material is of the viscose type, or the saponified acetate type, etc., and also whether the rayon is in filamentary or woven fabric or cloth form, etc. It will also be noted from these same examples that the heating rates which may be employed in the present invention, with the obtainment of very good properties, may typically be as follows:

Room temperature to 350 C.about l000l300 C./hr. 350 C. to 800 C.about 2500-2700 C./hr. 800 C. to 2800 C.about 10,00012,000 C./hr.

It will also be noted that the starting materials and processing conditions in Examples 5 and 6 are exactly the same as in Examples 1 and 2 except for the omission of the intermediate flexing step of this invention. The advantages and product improvements realizable because of the step of this invention are readily apparent.

Examples 7 and 8 point up the criticality of the temperature range to which the cloth must be heated before it is flexed. If the cloth is heated to too low a temperature and then flexed, as in Example 7, or heated to too high a temperature and then flexed, as in Example 8, the product improvements are not obtainable, even though substantially identical heating schedules and processing conditions are otherwise followed.

Example 9 points up the fact that even though much slower heating rates to 350 C. are employed than in Example 1, because of the omission of the flexing step, the product qualities obtained are still not as good as those obtained in Example 1.

Example 10 demonstrates that product properties comparable to those obtained in Example 1 are obtainable without employing the flexing step, but that very greatly prolonged heating rates or times must be employed in order to accomplish this.

If the rayon being processed is in filamentary form or if its width is of relatively small dimension then flexing in substantially only one direction, or longitudinal of the material, is generally all that is necessary. However, if the rayon is in the form of a woven fabric or cloth, having both warp and fill filaments, or is of substantial width, then flexing in both longitudinal and transverse directions are necessary to achieve optimum results and to insure the obtainment of a carbonized or graphitized product strong or flexible in one direction, and not noticeably weaker or less flexible, etc., in the other direction.

By flexing is meant working or ruffling or pressing the rayon, after it has been heated to a suitable temperature, until it is soft or supple or very flexible. (The heattreated rayon at this point, before being flexed, is generally fairly stiff or rigid and also coarse to the touch rather than soft.) A typical way of flexing the cloth can be accomplished by the use of standard commercially available calender rolls, such as used in textile operations, with the only limiting factor being the pressure applied by the rollers, such that the cloth is not physically damaged; but sufficient pressure is employed to render the cloth supple and flexible.

For convenience in handling, etc., the rayon which has been heated to a suitable temperature, will typically be cooled to temperatures below about C. or to room temperatures before the flexing step is carried out; however, this is not absolutely essential to the invention.

After the flexing step has been carried out, the heattreated and flexed rayon may be heated substantially immediately or over a very short time period to the temperature it had previously been heated to before it was flexed; thereafter, it may be heated to carbonizing or graphitizing temperatures following any convenient timetemperature schedules, such as outlined in the examples.

The flexing can be accomplished by hand simply by working the product between the palms of one or more persons until the hand or feel of the material is proper; or it can be accomplished by passing the heattreated rayon between two opposed rollers one or more times until suflicient flexibility is effected. Rubber or plastic coated rollers are preferredeither one rubber, etc., with one steel or metal roller, or both rubber or plastic coated.

It should be understood that slower heating rates, than those previously pointed out as typical, may also be employed. However, rates slower than 200 C. per hour, in going from room temperature to the 325-390 C. range, or in going to the further carbonization temperature (which is exemplified as 800 C., but which typically may be anywhere between about 500 C. and about 1200 C.) will seldom be employed because inexpedient and because of the prolonged processing times involved.

It is also to be understood that the invention is not limited to the specific examples which have been offered merely as illustrative and that modifications may be made within the scope of the amended claims without departing from the spirit of the invention.

We claim: 1. A process of carbonizing rayon which comprises: heating the rayon under substantially non-oxidizing conditions to a temperature between 325 C. and about 390 C.;

interrupting the heating step at a temperature in this range and flexing the rayon by mechanically or manually working the product to make it more supple; and

continuing the heating of the rayon under non-oxidizing conditions to a temperature above about 500 C. to further the carbonization thereof. 2. A process according to claim 1 wherein the rayon is heated from room temperature to the 325 C.-390 C. range at a rate no slower than 200 C. per hour, and wherein the flexed material is then further carbonized at a rate no slower than 200 C. per hour.

3. A process according to claim 1 wherein the flexing of the rayon is carried out after it has been cooled to a temperature no higher than about 40 C.

4. A process according to claim 1 wherein the final temperature to which the rayon is heated is between about 500 C. and about 1200 C.

5. A process according to claim 1 wherein the initial temperature to which the rayon is heated before it is flexed is between about 340 C. and about 360 C.

6. A process according to claim 1 wherein the rayon is viscose rayon.

7. A process according to claim 1 wherein the rayon is in the form of a woven fabric.

8. A process according to claim 7 wherein the flexing of the woven fabric is carried out in directions both longitudinal and transverse to the fabric.

9. A process of graphitizing rayon which comprises: heating the rayon under substantially non-oxidizing conditions to a temperature between about 325 C. and about 390 C.;

interrupting the heating step at a temperature in this range and flexing the rayon; by mechanically or manually working the product to make it more supple and continuing the heating of the rayon under non-oxidizing conditions to a temperature between about 2000 C. and about 3000 C.

References Cited by the Examiner UNITED STATES PATENTS 3,011,981 12/1961 Soltes 252502 3,107,152 10/1963 Ford et a1. 23209.2 3,116,975 1/1964 Cross et a1 23209.4

OSCAR R. VERTIZ, Primary Examiner.

E. I. MEROS, Examiner. 

1. A PROCESS OF CARBONIZING RAYON WHICH COMPRISES: HEATING THE RAYON UNDER SUBSTANTIALLY NON-OXIDIZING CONDITIONS TO A TEMPERATURE BETWEEN 325*C. AND ABOUT 390DC.; INTERRUPTING THE HEATING STEP AT A TEMPERATURE IN THIS RANGE AND FLEXING THE RAYON BY MECHANICALLY OR MANUALLY WORKING THE PRODUCT TO MAKE IT MORE SUPPLE; AND CONTINUING THE HEATING OF THE RAYON UNDER NON-OXIDIZING CONDITIONS TO A TEMPERATURE ABOVE ABOUT 500*C. TO FURTHER THE CARBONIZATION THEREOF. 